Stent

ABSTRACT

A stent shaped as a three-dimensional body which is formed by interlaced threads (1) arranged in multistart turns of a helical line. The threads (1) are arranged in at least two groups (2 and 3) of the helical turns featuring opposite senses of helix. The stent ends are established by sections (5) where the turns of one helical line merge into those of the other helical line, said sections appearing as a single length of the thread (1).

TECHNICAL FIELD

The present invention relates in general to medicine and morespecifically to surgery and can find predominant application forendoreconstruction of blood vessels and other hollow organs andstructures of human body. The invention also enables one to carry outreconstruction of perforating lesions.

BACKGROUND ART

Modern medicine is capable of reconstructing blood vessels, ducts, andperforating lesions of human organs, using special framework-typedevices named stents. Use of stents makes it possible to restore thenatural function of an defected anatomical structure without havingrecourse to direct operative interference techniques.

In order to function as an effective and reliable endoprostheses stentsmust possess a number of specific properties. First and foremost stentsmust provide unobstructed motion of body fluids through the implantedstructure. Such stents must be very flexible and at the same time mustbe rigid enough to withstand the pressure exerted by walls of bloodvessels or body cavities, with uniform pressure distribution over entireside of the stent. Moreover, the stent construction must be convenientfor being transported to the zone of reconstruction and positionedthere, as well as must not produce any injurious effect upon thesurrounding tissues in the course of implantation and furtherfunctioning.

One state-of-the-art hollow tubular stent is known to have end portionsand a surface formed by a plurality of intersecting elastic elements atleast part of which are interconnected at the stent ends (U.S. Pat. No.733,665).

The stent can be of two different diametrical dimensions due to radialdeformation of its elastic elements. Before being positioned at theplace of reconstruction the stent is deformed so as to minimise itsdiametrical dimension. Then the stent is placed, in the deformed state,inside a transporting means by arranging it on a special setting bulb.Once the stent has been transported to the place of reconstruction thesetting bulb is expanded so that the stent diameter is expanded to itsmaximal value.

It is due to its rigid construction that the stent withstands ratherhigh pressure of the walls of the organ being prosthesized and providesfor a uniform distribution of the resultant stresses over theprosthesized surface.

However, the stent in question features but lower elasticity due to arestricted axial deformation, which affects the quality ofendoprosthesizing.

Another prior-art stent is known to be in the form of a hollow tubularspringlike body made of a material having a shape memory effect (SME).Stents made from such a material are capable of restoring their shapeupon a change in the temperature conditions.

The advantages of said stent are determined by the properties of thematerial it is made from that provides for complete restoration of thestent shape in the zone of reconstruction, as well as a possibility ofits convenient withdrawal from the organ being prosthesized upon coolingof the stent. The procedure of the stent positioning is improved, too.

A variety of stent embodiments are possible. In particular, the stentmay have a construction disclosed in the aforediscussed invention (U.S.Pat. No. 733,665).

One more stent embodiment presents its construction as a hollow tubularelement established by the coils of a wire or the turns of a strip. Theconstruction of such a stent is more elastic since the stent isdeformable both radially and axially.

However, with this stent it is not always possible to provide andoptimum value of the pitch of spring coils or of strip turns becausewith too a large pitch a uniform pressure distribution over the surfacebeing prosthesized is affected, which may result in partial vesselstenosis, whereas in the case of too a small pitch stent implantationmay cause hyperplasia of the intima of the vascular wall in the organunder reconstruction, as well as early thrombotic complications.

Still more stent of the prior art is known to appear as athree-dimensional tubular structure established by a number ofinterlaced rigid and elastic threads arranged in two groups alonghelical lines directed oppositely to each other. Ends of these helicalthreads are not connected to one another or to helical portions of otherthreads but are arranged loosely at both ends of the tubular structure.

The stent under consideration is elastic and easily deformable, and canbe placed in a small-diameter delivery systems; besides, the stentprovides for an adequate rigidity and a uniform pressure distributionover the surface being proshesized.

However, the presence of free ends of threads on the stent end facesaffects adversely the framework properties as a whole. To attain therequired rigidity involves increasing the number of threads used, whichis undesirable since this may cause intimal hyperplasia and earlythrombotic complications. The ends of threads loosely arranged at theends of the tubular structure produce an injurious effect upon walls ofa blood vessel; in addition, more complex devices are required todeliver the stent to a required location inside a body.

Known in the present state of the art is a stent in the form of athree-dimensional structure formed by interlaced threads arranged inmultistart turns of a helical line (RU, A, 1,812,980). The turns form atleast two groups featuring opposite senses of the helical line. Thethread is made of a material featuring the SME. The ends of threadsbelonging to different groups are fixedly joined together on the endfaces of the three-dimensional structure by, e.g., spot welding orsplicing together.

The stent under discussion provides for a required rigidity and auniform pressure distribution over the surface being prosthesized, aswell as possesses elasticity.

It is due to joined together ends of threads on the stent end faces thatits placing into a transporting system is simplified. The selected stentmaterial ensures virtually complete restitution of its shape at theplace of the prosthesis implantation.

However, an artificial joining of threads results in a local change ofthe physic-mechanical properties of the stent, which tells negatively onthe rigidity and reliability of the stent construction as a whole.Moreover, the presence of artificial joints between the threads on thestent end faces gives one no way of attaining a maximum possible stenttransformation which in turn places limitation on a possibility of itsplacing into a small-diameter delivery systems.

DISCLOSURE OF THE INVENTION

The present invention has for its principal object to provide a stentwith a broad range of functional applications, possessing the requiredrigidity and elasticity, as well as a high degree of the shapetransformation.

The foregoing object is accomplished due to the fact that in a stentshaped as a three-dimensional body which is formed by interlaced elasticthreads arranged in multistart turns of a helical line and in at leasttwo groups featuring opposite senses of the helix line, according to theinvention, the ends of the three-dimensional body are established by thesections where the turns of one helical line merge into those of theother helical line, said sections appearing as a bend of a single threadsegment.

Thus, instead of joining the threads at both ends of the stent bywelding, soldering or other similar means, these ends are connected bycurvilinear segments made of the same piece of thread. Hence similarphysic-mechanical properties are retained in the entire stent volume,while the sections of the thread merging at the stent ends acquire theproperties of a spring and become the functionally active constructionelements. The stent ends formed by all the aforesaid sections of thethread bend are capable of withstanding the pressure of the walls of theorgan under reconstruction, and the stent construction acquires therequired rigidity so that the stent provides for a uniform pressure overthe surface being prosthesized. In addition, it is due to their elasticproperties that the section of the thread bend tend to restore theiroriginal shape after their having undergone deformation, thereby takingan active part in the process of the stent shape restoration.

The herein-proposed stent construction features the required elasticitydue to a possibility of its radial and axial deformation under theaction of small forces applied thereto.

The stent construction provides for high degree of the transformation ofthe stent shape. In the case of longitudinal stent deformation thethreads slide with respect to one another, with the result that theangle of their mutual arrangement changes, the stent diameter decreasesand becomes equal in length. Hence the stent diameter is much reduced,whereas its length changes but rather inconsiderably. High degree of thetransformation cenables one to place different-dimension stents into aminimised-diameter delivery systems, a future that solves the problem oftransporting stent to the place of reconstruction along both major andminor blood vessels.

To attain the maximum degree of the stent transformation with therequired construction rigidity remaining unaffected, it is expedientthat the turns of all the helical lines are made of a single threadsegment. Such a stent possesses high elasticity and transformationability due to a low interlacing density and a small number of threads.In addition, low interlacing density tells positively on the quality ofendoreconstruction because it reduces reaction of the walls beingprosthesized to a foreign body being implanted.

It is expedient in some cases that the stent features variable-pitchturns so as to provide different interlacing density as for the stentlength with a view to, eg.g., high-rate formation of the neointima ofthe vessel walls on individual reconstruction areas.

It is practicable that the stent is shaped as three-dimensional bodyhaving variable cross-section diameter as for the length thereof, afuture that makes it possible to obtain a stent shape adapted forendoreconstruction of defects of the various types and configurations.

Whenever it becomes necessary to obtain higher-density threadinterlacing on a preset area, it is expedient that the stent is providedwith additionally interwoven threads on said area. Such a stent isapplicable for, e.g., reconstructing an aneurysms vessel.

It is expedient that the free thread ends are joined on the surface ofthe three-dimensional body, to the threads that form helical turns,and/or to one another, thus adding to the stent reliability.

It is expedient that on the sections of merging, the turns of onehelical line merge into those of the helical line with the oppositesense of the helix. In this case, the radius of curvature of the mergingsection is increased, and such sections become more resilient.

A bend or curvilinear segment connecting two helical elements made fromthe same thread can have various shapes, e.g. of a circular arc, a loopor an U-shaped. Those merging sections are most elastic which are shapedas circle arcs having a large radius of curvature.

In some instances it is expedient that the points of bending the threadson the merging sections are arranged in different transverse planesrelative to the longitudinal body axis. This makes it possible to attainmore compact arrangement of the stent ends during its transformation.

It is expedient that the stent is made of a material possessing a SME orof a superelastic material. Such stent possess a virtually completedegree of shape restitution.

It is expedient that, with a view to reducing its thrombogenicity, insome instances the stent may be provided with a biocompatible material.

No sources of information have been found by the Applicants that wouldcontain any data on technical solutions identical or equivalent to thedevice proposed herein. This, in the Applicants' opinion, renders theinvention conforming to the condition of novelty (N).

Practical realisation of the specific features of the present inventionimparts an important technical effect to the stent, consisting in thatits required construction rigidity is attained along with highelasticity and transformation ability. The aforesaid novel feature ofthe present invention define, in the Applicants' opinion, conformity ofthe herein-proposed technical solution to the inventive step criterion(IS).

Practical use of the herein-proposed technical solution provides for anumber of positive properties that follow:

Required construction rigidity and uniform pressure distribution overthe surface being prosthesized;

High stent elasticity;

High degree of the shape transformation, which enables the stent to beplaced into a minimum-diameter delivery systems;

Lower traumatogenicity of the stent implanting procedure;

Broad range of functional applications.

BRIEF DESCRIPTION OF THE DRAWINGS

In what follows the present invention will now be disclosed in adetailed description of some illustrative embodiments thereof withreference to the accompanying drawings, wherein:

FIG. 1 is a general view of the proposal stent;

FIG. 2 shows an embodiment of the stent, wherein the bending points ofthreads on the merging sections are situated transverse planes relativeto the longitudinal axis of the three-dimensional body;

FIG. 3 shows another stent embodiment used as a filter;

FIG. 4 shows one more stent embodiment aimed at endoreconstruction ofperforating defects; and

FIG. 5 shows a stent embodiment aimed at endoreconstruction of aneurysmsvessels.

Referring now to the accompanying Drawings FIG. 1 presents a stent ofthe present invention appearing as a three-dimensional body made ofinterlaced elastic threads 1 arranged in multistart turns along ahelical line in two groups 2 and 3 featuring opposite senses of helix.The stent is made of a single segment of the thread 1 whose loose ends 4are joined together and to the threads 1 of the groups 2 and 3 byinterlacing. The stent ends are established by sections 5 of merging theturns of the thread 1 of the group 2 into the turns of the thread 1 ofthe group 3 and appear as a bend of the single segment of the thread 1.The bend of the thread 1 on the section 5 is shaped as a circle arc.

FIG. 2 presents a stent embodiment, wherein the bending points of thethreads 1 on the merging sections 5 are situated in different transverseplane's a1, a2, and b1, b2 with respect to the longitudinal stent axisand are arranged in an alternating order. The bends of the threads 1 onthe merging sections 5 are shaped as circle arcs. The stent is made froma single segment of the thread 1. Such an embodiment is preferable forlarge-diameter stents used in, e.g., endoprosthesizing the aorta, when aminimum diameter of the stent ends is to be provided in the deformedstate, the required rigidity of the stent construction remainingunaffected. The diameter of this stent can be reduced more than tenfoldthroughout its entire length. The number of turns of the thread 1 andtheir pitch are preset proceeding from the required interlacing density,which is so selected that the area S of meshes established by theintersecting helical turns provides the required rigidity, whereas themeshes should be large enough not to cause hyperplasia of the intima ofthe walls under reconstruction or earlier thromboses complications.

FIG. 3 presents a stent embodiment, wherein the cross-sectional diameterin the central portion of the three-dimensional body is much larger thanthe cross-sectional diameters of the stent ends. The stent isspherial-shaped and is aimed at use as a filter for, e.g., preventingthromboembolism of the pulmonary artery. The merging sections 5 at thestent ends are loop-shaped.

FIG. 4 presents a stent embodiment intended for reconstructing, e.g.,perforating injuries of the cardiac septa, or the open arterial duct.The stent has a minimum transverse diameter at the centre of thethree-dimensional body and the maximum possible transverse diameters atits ends. The stent dimensions are so selected that its length exceedsthe maximum diameter of a defect 6, and the diameter of the stent endsis such that the projection of the stent ends onto a wall 7 exceeds thearea of the defect 6. The dotted line indicates the shape assumed by thestent in the strained state. The stent is positioned in the strainedstate through a perforation of the defect 6. Once installed the stentrestores its original shape, whereby its end portions open up to theirmaximum diameter and are fixed outside the defect 6.

FIG. 5 presents a stent embodiment applicable in the case of ananeurysmal dilatation of a blood vessel. The stent is provided with theadditionally interwoven threads 1 on a section 8, which features ahigher interlacing density of the threads 1. This increase of densityfavorably influences neointima formation and is instrumental in blockingan aneurismal cavity 9 from a bloodstream in a vessel 10.

The herein-proposed stent operates as follows. A preliminarycatheterization of the afferent passages is performed under asepticconditions. A guide wire is inserted into the catheter, and the guidewire working end is placed outside the zone of reconstruction.

Then the catheter is withdrawn, whereupon the stent and the deliverysystem are fitted in succession onto the free guide wire end, saiddelivery system appearing as two coaxial catheters. Next the stent isdeformed by applying slight longitudinal forces to the stent ends, afterwhich the stent is placed into the free space of the outside catheter ofthe delivery system. Further on the assembled delivery system is broughtto the place of endoreconstruction under fluoroscopy control and isreleased. The stent assumes its original shape and is fixed reliably inposition.

Thus, the stent construction provides for its quick and convenientimplantation in the preset zone of reconstruction.

Industrial Applicability

The proposed invention is instrumental in attaining high-qualityreliable endoprosthesizing of blood vessels, ducts, and perforatingdefects of the various organs, which is confirmed by good clinicaleffects attained in implantation of the stents in cases ofocclusion-stenotic pathology of the blood vessels, vascular aneurysms,obstructions of the billiary ducts, and in portal hypertension (TIPS).

The aforelisted surgeries were conducted in St.Petersburg in 1992-1994on the basis of the Central Roentgenology and Radiology ResearchInstitute, the St.Petersburg State Medical Academy, as well on the basisof the Central Regional Clinical Hospital.

We claim:
 1. A stent shaped as a three-dimensional body having first andsecond ends and a side surface disposed between the first and secondends, the side surface being formed by two groups (2, 3) of elongatedelements (1), each of elongated elements (1) being formed from anelastic thread extending in a helical configuration along a longitudinalaxis of the said body, the elements of the first group having a commonfirst direction of winding and the elements of the second group having acommon second direction of winding opposite to the first direction,wherein:the elongated elements (1) of the first and second groups (2, 3)are axially displaced from the elongated elements of the same group; theelongated elements of the first group (2) are interwoven with theelongated elements of the second group (3) intermediate the first andsecond ends of the body; each elongated element from at least oneselected subgroup of the first group (2) and/or the second group is madeof the same thread as at least one other elongated element; and eachportion of the thread for connecting elements made of the same thread isformed as a curvilinear segment (5) having a length substantially lessthan a length of the body between the first and second ends and a shapeand orientation substantially different from shape and orientation ofany of the elongated elements (1).
 2. The stent as set forth in claim 1,wherein all elongated elements are made of a single thread (1).
 3. Thestent as set forth in claim 1, wherein the elongated elements (1) havevariable pitch along the length of the three-dimensional body.
 4. Thestent as set forth in claim 1, wherein the three-dimensional body has avariable diameter along its length between the first and second ends. 5.The stent as set forth in claim 1, wherein a portion (8) of the sidesurface is provided with third and fourth groups of the elongatedelements, the elongated elements of the third and the fourth groupsbeing formed by an elastic thread and extending in a helicalconfiguration along a longitudinal axis of the body, wherein:theelements of the third group have the common first direction of winding,are axially displaced from each other and interwoven with the elongatedelements of the second group; and the elements of the fourth group havethe common second direction of winding, are axially displaced from eachother and interwoven with the elongated elements of the second group. 6.The stent as set forth in claim 1, wherein free ends (4) of each of thethreads forming the elongated elements of the selected subgroup areinterlaced with at least one of the elongated elements (1), and/or witheach other.
 7. The stent as set forth in claim 1, wherein one elongatedelement of each pair of the elongated elements made of the same threadbelongs to the first group, and another elongated element belongs to thesecond group.
 8. The stent as set forth in claim 1, wherein at least apart of the curvilinear segments (5) at each end of thethree-dimensional body are bent at different angles outwards from aplane parallel to the longitudinal axis of the three-dimensional body.9. The stent as set forth in claim 1, wherein the threads forming theelongated elements (1) are made of a superelastic material.
 10. Thestent as set forth in claim 2, wherein the elongated elements (1) havevariable pitch along the length of the three-dimensional body.
 11. Thestent as set forth in claim 2, wherein the three-dimensional body has avariable diameter along its length between the first and second ends.12. The stent as set forth in claim 2, wherein a portion (8) of the sidesurface is provided with third and fourth groups of the elongatedelements, the elongated elements of the third and the fourth groupsbeing formed by elastic threads and extending in a helical configurationalong a longitudinal axis of the body, wherein:the elements of the thirdgroup have the common first direction of winding, are axially displacedfrom each other and interwoven with the elongated elements of the secondgroup; and the elements of the fourth group have the common seconddirection of winding, are axially displaced from each other andinterwoven with the elongated elements of the second group.
 13. Thestent as set forth in claim 2, wherein one elongated element of eachpair of the elongated elements joined by the curvilinear segment (5)belongs to the first group, and another elongated element belongs to thesecond group.
 14. The stent as set forth in claim 2, wherein at least apart of the curvilinear segments (5) at each end of thethree-dimensional body are bent at different angles outwards from aplane parallel to the longitudinal axis of the three-dimensional body.15. The stent as set forth in claim 2, wherein the thread forming theelongated elements (1) is made of a superelastic material.
 16. The stentas set forth in claim 3, wherein free ends (4) of each of the threadsforming the elongated elements of the selected subgroup are interlacedwith at least one of the elongated elements (1), and/or with each other.17. The stent as set forth in claim 3, wherein the three-dimensionalbody has a variable diameter along its length between the first andsecond ends.
 18. The stent as set forth in claim 3, wherein oneelongated element of each pair of the elongated elements made of thesame thread belongs to the first group, and another elongated elementbelongs to the second group.
 19. The stent as set forth in claim 3,wherein at least a part of the curvilinear segments (5) at each end ofthe three-dimensional body are bent at different angles outwards from aplane parallel to the longitudinal axis of the three-dimensional body.20. The stent as set forth in claim 3, wherein the threads forming theelongated elements (1) are made of a superelastic material.